The present invention relates to a color cathode ray tube provided with a reinforcing band for preventing implosion of a vacuum envelope.
In general, a color cathode ray tube is provided with a vacuum envelope of glass. The vacuum envelope comprises a substantially rectangular panel, which includes an effective portion and a skirt portion provided on the peripheral portion of an effective portion, and a funnel attached to an end face of the skirt portion as a sealed edge. A phosphor screen is formed on the inner surface of the effective portion of the panel. The screen is composed of three color phosphor layers that glow blue, green, and red, individually.
A substantially rectangular shadow mask is opposed to the inside of the phosphor screen. The shadow mask includes a substantially rectangular mask body and a substantially rectangular mask frame attached to the peripheral portion of the mask body. A large number of electron beam passage apertures are formed in an effective surface of the mask body that faces the phosphor screen. The shadow mask is supported by means of a mask supporting mechanism, which has stud pins and elastic support members. The stud pins are provided the skirt portion of the panel. The support members are fixed to the mask frame and engage their corresponding stud pins.
An electron gun for emitting three electron beams is disposed in a neck of the funnel. In the color cathode ray tube, the three electron beams emitted from the electron gun are deflected by means of a deflector, that is mounted on the outer surface of the funnel, so as to horizontally and vertically scan the phosphor screen through the shadow mask, thereby displaying a color image.
A reinforcing band is attached to the outer periphery of the skirt portion of the panel. The band constricts the skirt portion to apply compressive stress to it, in order to prevent implosion of the vacuum envelope. A practical example of the reinforcing band is of a shrunk-on type in which a previously looped band is expanded by heating and attached to the periphery of a skirt portion of a panel, and thereafter, the outer periphery of the skirt portion is shrunk to be constricted by cooling. Another example is of a type such that a belt-shaped band is wound around the outer periphery of a skirt portion of a panel and expanded by heating. Thereafter, in this case, the band is looped by welding its lap portions under tensile stress, and the skirt portion is shrunk to be constricted by cooling.
In the conventional color cathode ray tube, moreover, the reinforcing band is situated so as to overlap or externally surround the stud pins that support the shadow mask.
If the reinforcing band is located in this manner, however, the compressive stress that acts on the skirt portion of the panel varies depending on the circumferential position of the skirt portion. In particular, the compressive stress that acts in the diagonal direction of the panel at each corner of the skirt portion increases and indirectly influences the shadow mask that is supported inside the panel.
Usually, the outer peripheral length of the skirt portion of the panel and the inner peripheral length of the reinforcing band are subject to manufacturing errors, and temperature conditions for the thermal expansion of the band are subject to variations. Accordingly, the compressive stress from the reinforcing band that acts on each corner of the skirt portion in the diagonal direction of the panel fluctuates, so that beam landing on the three color phosphor layers is subject to variations.
In general, a color cathode ray tube that is fitted with the reinforcing band is attached to the housing of a TV set by means of lugs that are provided on the band. If the reinforcing band is situated overlapping the stud pins that support the shadow mask, therefore, voice vibrations from a loudspeaker of the TV set are transmitted to the shadow mask through the reinforcing band, stud pins, and elastic support members in engagement with the pins. The resulting resonance (microphonic vibration) of the shadow mask causes image disturbance.
In a color cathode ray tube that is provided with a flat panel having a flat or slightly curved effective portion, on the other hand, the curvature of the shadow mask is reduced corresponding to the effective portion, so that the strength of the mask is lowered. If only a small external force acts on the tube, therefore, the shadow mask is influenced considerably. Thus, the aforementioned problems are more serious to the color cathode ray tube of this type than to the conventional one.
The present invention has been contrived in consideration of these circumstances, and its object is to provide a color cathode ray tube, in which variations in beam landing attributable to variations in the compressive stress of a reinforcing band and image disturbance caused by resonance of a shadow mask can be reduced.
In order to achieve the above object, a color cathode ray tube according to the present invention comprises: a vacuum envelope having a panel, including a substantially rectangular effective portion and a skirt portion provided on the peripheral portion of the effective portion, and a funnel joined to an end edge of the skirt portion; a shadow mask including a substantially rectangular mask body and a substantially rectangular mask frame attached to the peripheral portion of the mask body, the mask body having an effective surface opposed to a phosphor screen on the inner surface of the effective portion and a large number of electron beam passage apertures formed in the effective surface; a mask supporting mechanism supporting the shadow mask and including stud pins arranged on the skirt portion and elastic support members fixed to the mask frame and engaging the stud pins, individually; and a reinforcing band constricting the outer periphery of the skirt portion.
The reinforcing band is arranged so as to fulfill a relation, bxe2x89xa72.0a, where a is the distance between first and second planes along a tube axis passing through the center of the effective portion of the panel, the first plane being in contact with the end edge of the skirt portion and extending perpendicular to the tube axis, the second plane containing the central axis of each of the stud pins and extending perpendicular to the tube axis, and b is the distance between the first plane and a third plane along the tube axis, the third plane being in contact with a side edge of the reinforcing band on the side remoter from the phosphor screen and extending perpendicular to the tube axis.
If the position of the reinforcing band relative to each stud pin is regulated in this manner, the reinforcing band, which constricts the skirt portion of the panel, never overlaps the stud pins that support the shadow mask, so that it never directly constricts those portions on which the stud pins are arranged. Accordingly, the shadow mask can be less influenced by compressive stress that acts on the skirt portion as the skirt portion is constricted by the reinforcing band. Thus, deviations in beam landing, which is attributable to variations in the compressive stress, can be lessened.
In the case where the color cathode ray tube is incorporated in a TV set, moreover, voice vibrations transmitted from a loudspeaker to the shadow mask can be attenuated to lower the possibility of resonance of the mask. Since no substantial load from the reinforcing band acts on those portions of the panel which are lowered in strength due to the presence of the stud pins, furthermore, the implosion-proof characteristic of the vacuum envelope can be improved.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.